This invention relates to a process for producing C.sub.5 -C.sub.40 hydrocarbons having a high paraffins content wherein mixtures of H.sub.2 /CO are contacted with supported ruthenium catalysts under process conditions to effect at least about a 20% CO conversion to hydrocarbon products.
The Fischer-Tropsch (F-T) synthesis reaction is well-known for producing a variety of hydrocarbon and oxygenated products by contacting H.sub.2 /CO mixtures with a heterogeneous catalyst, usually iron-based, under conditions of elevated temperature and pressure. The range of gaseous, liquid and solid hydrocarbon products that can be obtained include methane, C.sub.2 -C.sub.4 paraffins, gasoline motor fuel, diesel motor fuel and reforming fractions, heavy hydrocarbon waxes, and olefins. Hydrocarbon fractions which are enormously important, in light of the current world energy crisis, are the diesel motor fuel and motor gasoline cut, i.e., C.sub.5 -C.sub.20 hydrocarbons, and the C.sub.21 -C.sub.40 cut, which can be steam-cracked to yield light olefin feedstocks.
A commercial F-T operation conducted by SASOL is currently in operation in South Africa in combination with a coal gasification process. Gasoline and diesel motor fuel are produced by contacting H.sub.2 /CO mixtures between 150.degree.-300.degree. C. and 20-25 atmospheres with iron-based catalysts.
There is a constant search for new and improved catalysts and/or processes in F-T technology which will selectively yield the C.sub.5 -C.sub.40 hydrocarbon fraction, in higher yield, purity and conversion, and especially under process conditions which produce only small amounts of methane, i.e., a low methane-make.
Ruthenium catalysts are known to be active catalysts in F-T synthesis. It was discovered by Pichler (see H. Pichler, Brennstoff-Chem. 19, 226 (1938) and H. Pichler and H. Bufflet, Brennstoff-Chem. 21, 247, 273, 285 (1940) that Ru catalyst can produce from H.sub.2 /CO mixtures at low temperature and high pressures, very high molecular weight waxes of about MW 1000 and above, i.e., polymethylenes, having melting points of 100.degree. C. and above.
The reference, I&EC Product Res. & Devel. 4, 265 (1965) by F. S. Karn et al, describes the reactivity of ruthenium on alumina catalysts in producing hydrocarbons ranging from C.sub.1 -C.sub.30.sup.+. Illustrated are runs made at 21.4 atmospheres pressure, 300/hr. space velocity, temperature of 220.degree.-240.degree. C. and H.sub.2 /CO molar ratios of 1 to 4 resulting in % CO conversions of 46-82%.
U.K. patent application No. 2,024,246A describes a hydrocarbon synthesis process for hydrocarbons in the C.sub.5 -C.sub.12 range, in which mixtures of H.sub.2 /CO are contacted with a supported ruthenium catalyst, preferably on alumina at elevated temperature. A criticality of the process is described wherein the outlet CO partial pressure must be not less than 0.8 atmospheres at a process temperature of about 500.degree.-525.degree. K. and not less than 3.0 atmospheres in the temperature range of 525.degree.-550.degree. K.
In addition, there is described in the article, J. of Catalysis 57, pp. 183-186 (1979) selective C.sub.5 -C.sub.20 hydrocarbon production in Fischer-Tropsch processes utilizing ruthenium on alumina catalyst.